Waste tires have a high recovery rate as compared with those of general plastic products and are reused as a fuel mainly in cement mills. In recent years, however, use of tire rubber pieces or rubber powder as they are, that is, a rise in a so-called material recycling rate is desired, and a crush desulfurization method in which large shearing force is applied by means of a double screw extruder, a pulverization method and various desulfurization methods for crushed vulcanized rubbers are investigated as methods for reusing waste rubbers of waste tires, etc., but a problem that the energy costs grow high is involved therein.
Then, treatment by microorganisms is investigated as an energy saving method. Microbial treatment is carried out at a low temperature, and therefore it is a treatment method consuming least energy. In respect to the microbial treatment, a method by which hard rubber is efficiently subjected to decomposition treatment is proposed in Japanese Patent Application Laid-Open No. 194624/1997 and Japanese Patent Application Laid-Open No. 60793/1999. However, treatment methods intending to completely decompose rubber pieces are shown in both the patent applications, and nothing is described on how powder rubber effective for material recycling can be obtained.
An object of the present invention is to obtain powder rubber for obtaining a rubber composition which maintains better fracture characteristics and higher abrasion resistance as compared with a case where conventional powder rubber is used and which is obtained from a waste rubber by less energy, and a rubber composition blended with the same.